1. Field of the Invention
The present invention relates to a movable contact unit used for a control panel and the like of various electronic apparatuses, and the invention also relates to a method of manufacturing the same.
2. Background Art
With the recent trend of reduction in sizes and thickness of various electronic apparatuses, there is a continuous increase in number of portable and easy-to-carry apparatuses such as mobile phones, and this trend has been pushing ahead with development of such panel switches as featuring low profile with capability of yielding good tactile responses to actuations for use as control panels and the like of these apparatuses. A large number of the movable contact units now being employed are the type that uses movable contacts of dome-like shape formed of conductive metal plates having elasticity since they can provide reliable electrical contacts.
Referring now to FIG. 6 to FIG. 10, description is provided of a conventional movable contact unit of such type and a manufacturing method thereof as disclosed in Japanese Patent Unexamined Publication, No. 2002-245898.
Sectioned views among these drawings are enlarged dimensionally only in one direction along their thickness for the purpose of making the structures easily comprehensible.
FIG. 6 is a sectioned view of the conventional movable contact unit, and FIG. 7 is an exploded perspective view of the same. In these drawings, movable contact unit 4 comprises base film 1 having an insulating property and flexibility formed into a predetermined outer shape, and a plurality of downwardly opened dome-like movable contacts 3, of which upper surfaces are fixed to the underside of base film 1 with adhesive layer 2. Polyethylene terephthalate (hereinafter referred to as “PET”) is one example of materials used for base film 1, and a thin sheet of electrically conductive metal is used for movable contacts 3.
Movable contact unit 4 is pasted with adhesive layer 2 in a removable manner onto a surface of a release layer formed on an upper surface of insulative separator 5 made of PET or the like material. This prevents corrosion of movable contacts 3, and keeps adhesive layer 2 on the underside of base film 1 from accidentally adhering to other parts and collecting undesirable objects during transportation and storage.
In FIG. 6 and FIG. 7 here, separator 5 is illustrated as being rectangular in shape corresponding to the size of movable contact unit 4. It is the general practice, however, that separator 5 is formed into a belt-like strip to allow placement of a plurality of movable contact units 4, as shown in the perspective view of conventional movable contact units in FIG. 8, in the light of convenience for transportation and storage.
Movable contact units 4 of the above structure placed on the upper surface of separator 5 are manufactured in the following manner.
First, a required number of downwardly opened dome-like movable contacts 3 are fixed in their respective positions by adhering upper center surfaces thereof to adhesive layer 2 formed on the underside of base film 1.
Next, the entire surface of movable contact unit 4 is adhered to belt-like separator 5 made of an insulation film by using adhesive layer 2 on the underside of base film 1 in a manner to sandwich movable contacts 3, as shown in a sectioned view of FIG. 9 depicting a method of manufacturing the conventional movable contact unit, and this product is designated as work-in-process item 6.
Work-in-process item 6 is then placed with base film 1 side up and separator 5 side down on top of rubber sheet 8 of about 1 mm thickness laid on press table 7 made of a metallic material such as iron.
Press die 9 heated by a heater (not shown) and positioned above base film 1 is then moved down to heat and press (hereinafter described as “hot press”) work-in-process item 6 from the upper side of base film 1.
Press die 9 used here is so formed that a number of portions 9A corresponding to movable contacts 3 are hollowed to avert hot pressing upon areas occupied by movable contacts 3. Flat face 9B thus shaped is capable of pressing the entire surface of work-in-process item 6 except where movable contacts 3 are disposed.
The hot press is carried out under the conditions of 80 to 130° C. in temperature and 0.1 to 0.3 MPa in pressure for 1 to 3 seconds, to complete the manufacturing process of movable contact unit 4 affixed to separator 5.
The hot press carried out in the above manner can bring base film 1 into close adhesion to movable contacts 3 along the dome-like shape, while also preventing base film 1 from coming off separator 5 in areas around the outer rims of movable contacts 3. This method ensures flat surface portions of a sufficient area between adjoining movable contacts 3 for adhesion with separator 5 even when movable contacts 3 are arranged closely with respect to one another. Accordingly, this method achieves consistency of the fixing positions of movable contacts 3 as well as steadiness of adhesion by way of increasing an overall area of adhering surface when movable contact unit 4 is bonded to a wiring board.
A plurality of movable contact units 4 adhered in this manner are arranged at regular intervals on belt-like separator 5, as shown in the perspective view of conventional movable contact units 4 in FIG. 8, and they are transferred by means of pilot holes 5A provided at regular intervals along separator 5. As movable contact units 4 are transferred, the process of hot press is carried out on the entire surface of press-on portion 10 of base film 1 except for the areas where movable contacts 3 are disposed
FIG. 10 is a sectioned view of a conventional switch that uses movable contact unit 4. Switch 15 comprises movable contact unit 4, which is removed from separator 5 and bonded to an upper surface of wiring board 11. Movable contact unit 4 is bonded to wiring board 11 in a position that outer rims of constituent movable contacts 3 lie on outer stationary contacts 12B, and lower center surfaces of movable contacts 3 confront respective center stationary contacts 12A with a predetermined space between them.
Switch 15 constructed as above is used for a portable information-handling device requiring a low-profile structure such as a mobile phone, for example. When this is the case, the switch is placed inside an enclosure case in a manner that the movable contacts are located behind dial buttons and the like, and connected to a control circuit so that the control circuit detects and executes communication control and the like tasks when the dial buttons are pushed.
In the structure discussed above, when a certain amount of pressing force is applied to movable contact 3 from the upper surface of base film 1, movable contact 3 elastically deforms downward into an inverse shape with a tactile click, and the lower center portion of movable contact 3 comes in contact with center stationary contact 12A. This establishes an electrical continuity between center stationary contact 12A and outer stationary contact 12B via movable contact 3.
When the pressing force is removed thereafter from the upper surface of base film 1, movable contact 3 elastically deforms upward into the original shape by its own elastic restoring force. This results in separation of the lower center portion of movable contact 3 from center stationary contact 12A to resume the electrically open state between center stationary contact 12A and outer stationary contact 12B.
In this conventional movable contact unit and the manufacturing method, base film 1 can be processed by the hot press to deform it along the dome-like shape down to the rims of movable contacts 3 since both base film 1 and separator 5 are formed of film materials such as PET. On the other hand, however, there occurs a small extent of deformation in any of base film 1 and separator 5.
An extent of the deformation is not so significant for each set of movable contact unit 4 that it hardly causes any problems in the process of manufacturing when only one set of movable contact unit 4 is adhered onto separator 5. When a plurality of movable contact units 4 are adhered onto separator 5, however, even a small deformation developed in separator 5 can accumulate. As a result, there emerges a substantial deviation in positions of pilot holes 5A used as the reference in a process of forwarding separator 5 from the press table after the hot press, thereby giving rise to a problem of decreasing productivity of movable contact units 4.
There is also a drawback with the above configuration wherein the plurality of movable contact units 4 are disposed at regular intervals on the belt-like separator 5, that a positional correction needs to be repeated frequently due to a cumulative increase in the positional deviation of pilot holes 5A when movable contact units 4 are mounted continuously onto wiring boards 11. This poses another problem of decreasing the efficiency of producing electronic apparatuses.